During launch of a payload, such as a spacecraft or satellite, the dynamic loads are a major design factor in the structural design of the payload. Launch survival often is a more difficult design problem than is the problem of ensuring operational performance in orbit. A significant percentage of payload malfunctions occur during launch, and those malfunctions are often due to vibration and acoustic loads.
A traditional design approach to enhance launch survival percentages involves structural stiffening. This approach, however, adds weight to the overall design and actually can lead to design features that are liabilities once the payload is in orbit. Although the current design techniques of providing semi-rigid payload attachment fittings for securing a payload to a launch vehicle avoids inducing lower frequency flexible body modes into the coupling structure between the launch vehicle and the payload system, they cause severe acceleration loads to be transmitted through the coupling from the engine as well as from other vibrational energy sources.
A conventional payload attachment typically provides a "hard mount" that effectively transmits all structural forces from the launch vehicle into the payload over a wide frequency band. A "whole-spacecraft" isolation system, in contrast, would replace the hard mount with a soft mount that would filter many of the forces of the frequency spectrum.
Most payloads are cantilevered on the launch vehicle and are attached to the launch vehicle only at the base of the spacecraft. The isolation problem thus is augmented because of the large ratio of center-of-gravity height to attachment width. Reduction of the axial attachment stiffness will introduce low frequency payload pitch and yaw modes with large acceleration force displacements at the upper end of the payload. This is undesirable because it may cause guidance control system instability.
Launch vehicles often have closely spaced flexure modes with frequencies as low as 1 Hz. A payload may have modes with frequencies starting as low as 6 Hz. The isolation of a 6 Hz payload from a 1 Hz launch vehicle is made more feasible using a "whole-spacecraft" acceleration force isolation system design approach.
The force transmission path for both dynamic and acoustic launch loads to the payload through a stiff attachment fitting has a detrimental impact on launch survival and the life cycle performance of the payload. There is a need, therefore, to replace the traditional design approach, which requires structural stiffening and component isolation, on a case-by-case basis with a "whole-spacecraft" isolation approach in the development of a reduced vibration environment for the payload. This would make it possible for several subsystems, such as solar panels and other flexible structures, to be made lighter. This would allow a larger percentage of the payload weight to be dedicated to scientific and commercial equipment. The isolation system also should allow for tuning of the isolator to meet any special design requirements. A whole-spacecraft design approach, furthermore, would reduce weight and cost as well as increase life and reliability.